On the opening night on KCON, the relative tameness of live sets from South Korean boy bands such as B1A4, Vixx and Teen Top suggested that K-Pop artists playing the U.S. are still figuring out how to live up to the wonderful insanity of their music videos.

On the second night of the festival, they might have found an answer: Just add more members. Or instruments.

Bangtan Boys, or BTS, is a fast-rising combo that (like many K-Pop acts) sees no distinction between hip-hop style and pop accessibility. The seven-member group has riffed on Kendrick Lamar's "Swimming Pools (Drank)" but also mastered the nuances of high-stepping dance routines and matching suits.

Their more rap-centric singles such as "Bulletproof" had drill-team precision in choreography and delivery, and the group made the strongest impression of all the U.S.-debuting acts. This won't be the last time they play to thrilled crowds in the States.

SPICA had similar designs. The girl group debuted its first English-language single, "I Did It," onstage at KCON, and it hit all the notes of a U.S. summer pop single -- a bit of '90s R&B, a bit of electro shine, a bit defiant in the lyrics. Their other singles are as likely to be informed by '60s soul as K-Pop dance beats, and they wrote "I Did It" with American producers. As an introduction for newcomers, SPICA is a fine ambassador for today's variety of K-Pop sounds.

Two rock acts, CN Blue and Jung Joon-Young, are only nominally K-Pop in the sense that they are South Korean and write quick, catchy singles in their home language. But each owed more to U.S. and British acts than anything coming out of the K-Pop production mines. Jung Joon-Young makes overt moves to rock aesthetics -- as if to underscore the point, his set was greeted by a digital banner reading "I Am a Korean Rocker" -- and though his set started a little modestly and tentatively Coldplay-ish, by the end he was covering Michael Jackson's "Black or White" and swinging his hips like Mick.

Speaking of moves like Jagger, CN Blue was one of the first South Korean acts of this wave of K-Pop to tour in the U.S., and the hard work showed. Their Maroon 5-indebted lite-funk went down easily and they looked great doing it. Though it wasn't the most progressive sound to be coming out of South Korea today, CN Blue played with a zest and presence that kept the crowd on its toes.

That same crowd was on its feet for Girls Generation, one of the landmark groups of "hallyu" now celebrating its seventh anniversary (a geologic time frame in K-Pop). All that touring has paid off handsomely. Songs such as "Mr. Taxi" and "Mr. Mr." sounded spry and adventurous. Even though they were down one member for this show, the group members understand how their individual chemistry adds up to one of the most charismatic presences in K-Pop.

And of course they played "Gee," and of course it was a sugary delight. K-Pop doesn't need to translate itself to Western audiences, but sometimes the old pop virtues hold up everywhere.

“I’m going to take a moment just to drink it all in,” Paul McCartney said Sunday night as he looked out on some 50,000 people in front of him in a sold-out Dodger Stadium, the venue where he performed 48 years earlier with the Beatles.